People suffering from Obstructive Sleep Apnea (OSA) and related conditions experience many A/H episodes during sleep. The conventional treatment for OSA is the well known Continuous Positive Airway Pressure (CPAP) treatment. An A/H episode often has an associated arousal, which is a nervous system response to low blood oxygen level and/or high blood carbon dioxide level.
The condition of OSA normally is diagnosed by laboratory based polysomnography (PSG). PSG involves the measurement of sleep and respiratory variables including EEG, EOG, chin EMG, ECG, respiratory activity, nasal airflow, chest and abdominal movements, abdominal effort and oxygen saturation. The data gathered leads to a calculation of the Respiratory Disturbance Index (RDI) which is the average number of arousals per hour due to respiratory disturbance. PSG is uncomfortable for a patient due to the placement of numerous electrodes on the patient's head or face and the wearing of a mask or nasal prongs. PSG is an expensive procedure and has the inconvenience of requiring the patient to attend a sleep clinic for a whole night requiring continuous technician attendance.
In the clinic, cortical arousals can be detected by measuring and interpreting, either automatically or by eye, changes in the patient's EEG and EMG. Arousals are an important indicator of the amount and quality of sleep obtained by a patient and the degree of severity of the patient's apneas.
To obtain a display of the EEG, electrodes must be attached to the patient's head and the signals from these electrodes passed through high gain amplifiers before subsequent display and recording. This is often inconvenient and time consuming; the signals also can become distorted or disappear due to electrode dislodgement or other artefacts such as sweating. To detect an arousal, the EEG, once displayed, requires interpretation either visually by a skilled operator or automatically by a computer-based analysis system. Apart from the difficulties of attaining accurate EEG data, EEG apparatus also is relatively more expensive than much other biomedical apparatus.
EEG data on its own is not an accurate determination of the occurrence of A/H episodes--an arousal can be due to other factors as noted.
Prior art disclosures that form background information to the present invention include (a) R. Ferber, et al, "ASDA Standards of Practice--Portable Recording in the Assessment of Obstructive Sleep Apnea", Sleep, 17(4): 378-392, 1994; (b) L. Ferini-Strambi, et al, "Heart rate variability during sleep in snorers with and without obstructive sleep apnea", Chest, 102(4): 1023-7, October 1992; and (c) C. Guilleminault, et al, "A review of 50 children with obstructive sleep apnea syndrome", Lung, 159:275-287, 1981.